brine disposal from reverse osmosis desalination plants in oman …atominfo.ru/files/brine/brine...
TRANSCRIPT
DESALINATION
ELSEVIER Desalination 133 (2001) 135-147 www.elsevier.com/locate/desal
Brine disposal from reverse osmosis desalination Oman and the United Arab Emirates
plants in
Mushtaque Ahmed”, Walid H. Shayyab*, David Hoey”, Juma Al-Handaly” aDepartment of Soil and Water Sciences; bDepartment of Bioresource and Agricultural Engineering
Sultan Qaboos University, Muscat, Sultanate of Oman ‘Department of Land and Water Conservation, New South Wales, Australia
Received 29 May 2000; accepted 2 October 2000
Abstract
Reverse osmosis (RO) desalination plants are used for supplying potable water to small communities in inland areas of Oman as well as small to large communities in the United Arab Emirates (UAE). Most of these desalination plants use brackish groundwater as feedwater. The production ofbrine (also known as concentrate or wastewater) is an integral part of the operation of desalination plants. Ten small-scale desalination plants in the interior parts of Oman and eight RO plants in the coastal areas of the UAE were investigated with regard to their brine disposal methods. The capacity of the Omani plants varied from 50 m3/d to a maximum of 1000 m3/d. The salinity level of wastewater varied from 9.8 to 6 1.2 dS/m (1 dS/m = 640 mg/L,). Various disposal methods were observed. These included lined evaporation ponds, ocean/beach disposal, and unlined small bores. The depth to the water table in the areas ofthe investigated desalination plants varies f?om 40 to 80m, while the average distance between feedwater intake and disposal areas was approximately 200 m. In the UAE, the capacities of the investigated plants varied between 950 to 15,000 m3/d. All the UAE plants dispose of their brine in the sea, although some of the plants dispose of their brine in nearby creeks that are linked to the sea. The chemical characteristics of the brine, feedwater, product water, and water from evaporation ponds (or bores) were determined. The presence of other chemicals including iron, copper, zinc, and cleaning agents (such as hydrochloric acid, sodium hexametaphosphate, and anti-Scala&) is likely to pollute the groundwater, if the brine were to reach the underlying aquifers. Under certain conditions, brine from the desalination plants can have useful applications. Potentials for such applications are addressed in this paper.
Keywords: Oman; UAE; Desalination; Wastewater; Evaporation ponds; Concentrate disposal; Brine; Reverse osmosis
*Corresponding author. New address: Agricultural Engineering Department, Marshall Hall, SUNY Morrisville, Morrisville, NY 13408, USA. Tel. +l (3 15) 684-6526; email: [email protected].
001 l-9164/01/$- See front matter 0 2001 Elsevier Science B.V. All rights reserved PII: SO01 I-9164(01)00092-3
136 M. Ahmed et al. /Desalination 133 (2001) 135-147
1. Introduction
The Sultanate of Oman occupies the south- eastern corner of the Arabian Peninsula and is located between latitudes 16”40’ and 26”20’ north and longitudes 5 l”50’ and 59”40’ east. The country has a coastal line that extends more than 1600 km along the southeastern coast of the Arabian Peninsula. Oman is bordered on the north by the Gulf of Oman, on the east and south by the Arabian Sea, on the southwest by the Republic of Yemen, on the west by the Rub’ al Khali (the Empty Quarter) of Saudi Arabia, and on the northwest by the United Arab Emirates. The country’s territory also includes the northern tip of Musandam that juts between the Persian Gulf and the Gulf of Oman. This portion is separated from the rest of the country by the territory of the United Arab Emirates. The climate of Oman is generally hot and arid. However, the humidity along the coast is high. The average annual temperature is about 28.3”C. The average annual rainfall is generally less than 102mm. On the other hand, the UAE is a federation of seven states lying along the east central coast of the Arabian Peninsula. The states include Abu Dhabi, Ajman, Dubai, Al Fujairah, Ra’s al Khaymah, Sharjah, and Umm Al-Qwain. UAE is bounded on the north by Qatar and the Persian Gulf, on the east by the Gulf of Oman and Oman, and on the south and west by Saudi Arabia. Most of the inhabitants of the UAE live in either coastal towns or inland oases. The rest of the UAE is sandy and unproductive. The climate is extremely hot and humid in summer, with average maximum temperatures exceeding 40°C. Winters are mild, and the average rainfall is very low.
Both Oman and the UAE are arid countries with hot dry climates. The per capita demand for fresh water is high, especially for domestic, agriculture, and industrial purposes. This demand increased dramatically along with the improve- ment and development of living standards [ 11.
Agriculture uses the lion share of water in Oman (approximately 90% of country’s total water use). Groundwater resources have been over-exploited resulting in seawater intrusion in coastal aquifers. To meet the demand for domestic water, the Omani government opted for the establishment of several desalination plants. In the 1980s and 199Os, desalination plants were built in inland rural areas. Most of these were RO plants of small capacities. The development of the desalination industry followed the same pattern in the UAE. Given the high standard of living in the UAE, the per capita consumption of water is also very high. The UAE desalination plants supply the major share of domestic water needs while some other plants even supply water for agricultural use.
Disposal of brine (also referred to as mem- brane concentrate, reject brine, and wastewater) in RO plants is of much significance both from economic and environmental standpoints. Improper surface disposal has the potential for polluting the groundwater resources that are used as feedwater for many of the RO plants. The groundwater pollution is likely to result from high salinity and the presence of other harmful chemicals in the brine. Khordagui [2] identified the following options for disposal of reject brine from inland RO desalination plants: pumping into specially designed lined evaporation ponds, deep- well injection, disposal into surface water bodies, disposal through pipelines to municipal sewers, concentration into solid salts, and irrigation of plants tolerant to high salinity (halophytes). Mickley et al. [3] identified the factors that influence the selection of a disposal method. These include the volume or quantity of concen- trate, quality or constituents of concentrate, physical or geographical location ofthe discharge point of the concentrate, availability of receiving site, permissibility of the option, public acceptance, capital and operating costs, and ability for the facility to be expanded. They also
M. Ahmed et al. /Desalination 133 (2001) 135-147 137
presented a survey of drinking water plants in the continental US (for drinking water membrane plants having a capacity of 98 m3/d or more) that included 137 plants where 48% dispose of the concentrate to surface water, 23% dispose to the head-works of wastewater treatment plants, 12% utilize a land application process, 10% dispose via deep well injection, and 6% use evaporation ponds.
According to ESCWA [4], cost plays an important role in the selection of a brine disposal method. This cost ranges from 5% to 33% of the total cost of desalination. The cost of disposal depends on the characteristics of reject brine, the level of treatment before disposal, means of disposal, volume of brine to be disposed of, and the nature of the disposed environment. Glueckstern and Priel [5] found that the disposal costs of inland RO desalination plants are higher than that of plants disposing reject brine in nearby seas or lakes.
Evaporation ponds can be successfully used for disposal of brine, especially in countries such as Oman and the UAE where hot and dry weather conditions prevail with high evaporation rates coupled with the availability of land at low cost. Sealing of evaporation ponds reduce the risk of groundwater contamination. Truesdall et al. [6] observed that evaporation ponds were used in some of the small desalination plants in the US. Evaporation ponds ranging from 13.6 to 34.3 ha are used for disposal purposes in the desalination plants in the central region of Saudi Arabia [7]. Mickley [S] considers evaporation ponds most appropriate for relatively warm and dry climates with high evaporation rates, level terrain, and low land costs. Squire et al. [9] described a method of surface water disposal of RO membrane concen- trate by blending the concentrate with backwash water from sand filters. Many small RO plants dispose their reject brine in municipal sewerage systems. This process has the attraction of lowering the BOD of the domestic sewage.
However, the increase in TDS may make it impossible to use the treated effluent for irrigation purposes.
The primary objective of this study was to assess the present status of disposal mechanisms of brine from RO desalination plants in Oman and the UAE as well as to explore alternative mechanisms for such disposals.
2. Methodology
Questionnaires were prepared to gather information and data. The questionnaires dealt with basic information and types of chemicals used in the desalination process. The plants targeted in Oman for the gathering of information included RO plants that utilize brackish groundwater as feedwater and have mostly land- based disposal methods to get rid of the brine. However, the plants investigated in the UAE disposed their brine into the sea. Relevant questionnaires were sent to government authori-
ties in Oman and the UAE. The Ministries of Electricity and Water in the Sultanate of Oman and the UAE responded with data and infor- mation on several desalination plants.
During field visits to desalination plants in Oman and the UAE, water samples were collected from feedwater, product water, and brine. Some samples were also collected from the standing water in evaporation ponds and disposal pits. Samples were analyzed for various chemicals and heavy metals at the Chemical Laboratory of the Ministry of Water Resources in Oman. Data on the use of chemicals in some of these plants were also collected. Most of the plants were government owned and used for domestic water supply. The method of disposal of brine in the visited 18 plants ranged from using evaporation ponds to the disposal in boreholes, shoreline, wadi beds, and ocean.
138 A4. Ahmed et al. /Desalination 133 (2001) 135-147
3. Results and discussion
The information presented in this paper was mostly gathered through field visits of 10 desalination plants in the Sultanate of Oman and the eight plants in the UAE, in addition to gathered information through a questionnaire survey. The following provides brief descriptions of the visited 18 desalination plants in Oman and the UAE as well as the cost of disposal of brine through evaporation ponds and the perceived challenges and opportunities of brine disposal methods.
3. I. Visited Omaniplants
Adam desalination plant: This plant started operation in 1997. It supplies water for domestic uses and has a capacity of 1000 m3/d. It is an RO plant with brackish groundwater as feedwater. The average recovery rate is 75%. The average quality of feedwater and concentration are 3.5 and 9.65 dS/m, respectively. The disposal method is evaporation ponds having the dimensions of 320 by 180 m. The evaporation ponds are 1368 m from the intake well. Polyethylene sheeting was used as liner in the pond. No salt build-up was observed in the ponds, which may be due to leakage.
Haima desalination plant: This plant started operation in 1996. The plant supplies water for domestic purposes with a capacity of 100 m3/d. It is also an RO plant that uses brackish ground- water as feedwater. The average recovery rate is 38%. The average feedwater salinity is very high (approximately 28.0dS/m). Consequently, the salinity level of the concentrate is also very high (approximately 43 .O dS/m). Evaporation ponds, each with the dimensions of 89 by 169 m, are used for disposal purposes. Polyethylene liners are used in the ponds. The feedwater well is nearly 200 m from the ponds. The observed lack of salt build-up in the ponds may be indicative of leakage.
Esherjah desalination plant: This plant started operation in 1996. It is also an RO plant supplying water for domestic purposes with a capacity of 100 m3/d. The average recovery rate is 42%. The average quality of feedwater is 42.5 dS/m and that of concentrate is 67.0 dS/m. Evaporation ponds with polyethylene liners are also used. Each of the ponds had the dimensions of 80 by 165 m. Some holes were observed in the liner and no salt build-up was noticed in the pond. The intake well is 290 m from the pond.
Sowqrah desalination plant: This plant is located near the beach and started its operation recently. It is an RO plant with a capacity of 100m3/d. The actual production has been less than the installed capacity of the plant due to the lack of demand. The feedwater is seawater and the concentrate is discharged into the sea. No environmental impacts were noticed.
Hitam desalination plant: This plant was commissioned in 1985. It is an RO plant supplying water for domestic purposes with a capacity of 1 00m3/d. It uses brackish ground- water as feedwater. The recovery rate is 25% while the average quality of feedwater is 20 dS/m and that of concentrate is 3 1 dS/m. The concen- trate is disposed in a small bore, approximately 200m from the intake well. The average groundwater depth is 40 m. It is highly likely that the disposed concentrate reaches the groundwater rather quickly.
Madrakah desalination plant: This RO plant is also located near the beach. The intake of feedwater is done through beach wells. It produces 100 m3/d ofwater for domestic purposes and 420m3/d of concentrate. The quality of feedwater is approximately 53dS/m and that of the concentrate is nearly 7OdSlm. The concen- trate is disposed on the beach, approximately 500 m from the intake wells.
Zahar desalination plant: This RO plant started operation in 1985. It has a capacity of 50m3/d and a recovery rate of 63%. The average
M. Ahmed et al. /Desalination 133 (2001) 135-147 139
quality of feedwater and concentrate are 5 and 14 dS/m, respectively. The concentrate is dumped in an unlined bore at a distance of 180 m from the intake. The groundwater table is located at 90 m from the surface. Because of the disposal practice, it is likely that the groundwater is being polluted.
10 X 20 m is used for concentrate disposal. The pond, lined with a PVC sheet, is located 100 m from the intake well. Salt is removed manually from the pond. The plant operators stated that environmental assessments were carried out and no adverse impacts were anticipated.
Assadanat desalination plant: This plant also started functioning in 1985. It is a RO plant with a capacity of 50m3/d. It uses brackish groundwater as feedwater with a recovery rate of 60%. The average quality of feedwater and that of concentrate are 10.2 and 20dS/m, respect- ively. The concentrate is dumped in an unlined bore at a distance of 200 m from the intake well. There exists risk of groundwater contamination. The plant operators stated that the groundwater table rises quickly after rainfall, possibly indicating that concentrate dumped in the bore is ultimately finding its way to the groundwater system.
3.2. Visited UAE plants
Qidfa I plant: The Qidfa I plant is located in Qidfa, the Fujairah Emirate. This RO plant began its operation in 1990 to supply water for domestic use. The capacity of the plant is 4550 m3/d. In 1997, 1.72~ 1 O6 m3 of water were supplied. Open seawater is used as feedwater and the average recovery rate is 40%. The average quality of feedwater and concentrate are 58 and 66 dS/m, respectively. The concentrate is disposed directly on the shoreline.
Abu-Mudhaibi desalination plant: This RO plant was established in 1985 for supplying water for domestic purposes. It has a capacity of 50m3/d and uses brackish groundwater with a recovery rate of 64%. The salinity of feedwater and concentrate are 8.4 and 23 dS/m, respect- ively. The groundwater is extracted from a depth of 40 m while the concentrate is disposed in a bore, 200 m from the intake well. The pit did not indicate any salt build-up. It appeared that most of the salt enters the groundwater system.
Qidfa II RO plant: The Qidfa II plant is also located in Qidfa. This RO plant began its operation in 199 1. It supplies water for domestic use and has a capacity of 9100 m3/d. In 1997, 2.58x 106m3 of water were supplied from the plant. Beach wells are used for supplying feedwater and the plant average recovery rate is 35%. On average, about 17,000 m3 of concentrate are produced every day. In 1997,6.2x lo6 m3 of concentrate were produced. The average quality of feedwater and concentrate is 56 and 66 dS/m, respectively. The concentrate is disposed directly on the shoreline.
Safah desalination plant: This RO plant is Kalba plant: The Kalba RO plant is located operated by the Occidental Petroleum Co. in in Kalba, the Emirate of Sharjah. The water is Oman. The plant is located in Safah, 130 km used for domestic purposes. The plant started from Ibri. It was constructed in 1983 with a operation in January 1995 and has a capacity of capacity of 100m3/d. The water is used for both 14,550 m3/d. Sixty-five brackish water wells are
domestic (major) and agricultural (minor) used for supplying feedwater to the plant. The
purposes. The groundwater is used as feedwater wells are scattered around the plant at distances
with a recovery rate of 50%. The depth to of 2.5 to 10 km. The plant is comprised of nine
groundwater table is approximately 100 m. The units. The average recovery rates of these units
average quality of feedwater is between 14 and vary between 65 and 70%. On average, the
20 dS/m. An evaporation pond of the dimensions volume of concentrate produced on a daily basis
140 M. Ahmed et al. /Desalination 133 (2001) 135-147
is more than 4550 m3/d. The average quality of feedwater and concentrate are 6 and 18dS/m, respectively. The concentrate is dumped back into the sea given its proximity to the plant.
Umm Al-Qwain water desalination plant: This RO plant is located in the Emirate of Umm Al-Qwain. The plant started operation in 1985 and provides 10,500 m3/d of desalinated water. After blending with brackish water, the plant can supply up to 15,000 m3/d. Sand filtration is done before the start of desalination. In 1997, the total volume of water supplied was 3.686~ lo6 m3. Groundwater from Sirrah well field, located 14 km from the plant, is used as feedwater. The average recovery rate is 75% and the average volume of daily concentrate produced is 3480m3/d. The average quality of feedwater and concentrate are 4.6 and 14.6 dS/m, respectively. The concentrate is first dumped in the Umm Al- Qwain creek by gravity pipes. Ultimately the concentrate reaches the ocean. The depth to the underlying groundwater table in the aquifer is about 30 m.
Jabal Al-Dhana plant: This RO plant is located in Jabal Al-Dhana of Abu Dhabi. The plant started operation in June 1991. Desalinated water from the plant is intended mostly for agricultural and domestic purposes. The capacity of the plant is 9 100 m3/d. Open seawater is used as feedwater and the recovery rate is approxi- mately 30%. The average salinity of feedwater is around 65 dS/m while the salinity of concentrate is 80 dS/m. The latter is directly dumped into the sea.
Hamriyah desalination plant: This RO plant is located in the Emirate of Sharjah. The plant started operation in 1995, with additional units being added in 1997. The produced water is used for domestic purposes. The capacity of the plant is 2900 m3/d. Brackish groundwater is used as feedwater and the supply wells are located 12 km from the plant. The average recovery rate is approximately 70%. The average volume of
concentrate produced is 870 m3/d. The average salinity of feedwater and concentrate are 3.2 and 10.5 dS/m, respectively. The concentrate is dumped in a nearby creek. Since the aquifer is away from this creek, no harmful effects are anticipated.
Al-Aryam plant: This RO plant is located in the western part of Abu Dhabi. The plant started its operation in 199 1. The water supplied from this plant is used for agricultural and domestic purposes. The capacity of the plant is 950 m3/d. Seawater is used as feedwater and the recovery rate is approximately 30%. The salinity level of concentrate is approximately 80dS/m, which is being dumped directly into the sea.
Al-Rafeek plant: This RO desalination plant is located in the western part of Abu Dhabi. Water from the plant is used for agricultural purposes. The recovery rate of the plant is 30% (design), although the actual recovery rate is less than 22%. The capacity of the plant is 950 m3/d. The plant treats seawater and the concentrate with a salinity level of 90 dS/m is being dumped back into the sea.
4. Chemical analysis
Tables 1 and 2 contain brine characteristics data of some selected small-scale desalination plants in Oman and the UAE. These data were obtained from a single sampling of water and brine from various RO desalination plants during field visits. As such, the data may not reflect the average characteristics of brine. Table 3 provides a summary of observed brine disposal methods in the plants visited. Table 4 shows the ratios of major ions of feedwater and brine of some Omani plants. The concentration of major ions in the brine appears to be proportional to those measured in the feedwater. This indicates that the process of desalination does not lead to the enrichment ofreject brine with any particular ion.
Tab
le
1
Che
mic
al
and
heav
y m
etal
ch
arac
teri
stic
s of
bri
ne
from
de
salin
atio
n pl
ants
in
Om
an
Para
met
er
Nam
e of
the
pla
nt
Ada
m
Hai
ma
Esh
eria
h So
war
ah
Hita
m
Mad
&ah
Z
ahar
A
ssad
anat
A
bu-M
udha
ibi
Safa
h
Che
mic
al c
hara
cter
isti
cs:
Cal
cium
(m
a)
417
Mag
nesi
um
(mg/
L)
280
Sodi
um
(mg/
L)
1670
Pota
ssiu
m
(mg/
L)
43.1
Stro
ntiu
m
(mg/
L)
13.1
PH
5.56
Car
bona
te
(mg/
L)
-
Bic
arbo
nate
(m
g/L
) 37
Chl
orid
e (m
giL
) 19
64
Sulp
hate
(m
g/L
) 43
36
Nitr
ate
as N
O9
(mg/
L)
5.2
Fluo
ride
(m
g/L
) -
E.C
(m
S/cm
) 98
70
S.A
.R
(me/
L)
15.5
1
S.E
.R
(me/
L)
61.7
7
Lan
gelie
r In
dex
(me/
L)
-1.8
6
Ryz
ner
Inde
x (m
e/L
) 9.
27
TD
S (
ma)
87
47
Tot
al
ions
(m
g/L
) 87
65
Tot
al
alka
linity
(m
g/L
) 30
Tot
al
hard
ness
(m
g/L
,)
2211
Hea
vy m
etal
cha
ract
eris
tics
:
Iron
(m
g/L
) 0.
06
Man
gane
se
(mg/
L)
0.07
Cop
per
(mg/
L)
< 0
.05
Zin
c (m
g/L
) <
0.0
5
Chr
omiu
m
(ma)
<
0.0
5
1020
406
5250
174.
0
23.9
3.07
- - 90
90
3881
- - 28
000
- - - - - - - - 0.14
< 0
.05
< 0
.05
< 0
.05
< 0
.02
841
625
1900
18
30
14,8
00
14,6
00
631.
0 66
8.0
18.3
12
.4
6.94
7.
94
- -
221.
0 -
24,0
62
-
6139
48
24
5.50
-
- -
61,1
00
60,5
00
64.6
5 -
75.0
1 -
0.63
-
5.68
-
48,5
10
-
48,6
18
-
181
203
9951
-
0.43
0.
41
0.05
0.
05
< 0
.05
< 0
.05
< 0
.05
< 0
.05
< 0
.02
< 0
.02
665
611
612
923
962
448
1980
31
5 41
3 44
8
4250
15
,300
19
80
2780
46
30
145.
0 68
5.0
95.4
81
.5
101
15.3
11
.4
16.3
28
.2
26.9
7.66
7.
07
7.32
7.
21
6.03
-
- -
-
173
125
859
464
8118
24
,802
43
67
4532
2466
38
46
1143
15
52
46.7
6.
1 24
.2
7.2
- 205
77,3
35
3296
56.4
-
- -
-
21,4
00
61,2
20
12,2
30
16,8
00
30.5
67
.68
16.2
1 19
.12
70.9
9 75
.93
59.3
9 59
.55
1.14
0.
32
1.47
1.
24
5.37
6.
43
4.38
4.
73
16,1
42
47,3
05
8990
10
,553
16,2
27
47,3
67
9412
10
,781
142
102
704
380
3526
96
98
2846
40
41
- 23,4
00
30.9
2
69.7
2
-0.3
3
6.68
16,9
60
17,0
61
168
4281
0.10
0.05
< 0
.05
< 0
.05
< 0
.02
0.43
0.05
< 0
.05
< 0
.05
< 0
.02
< 0
.05
< 0
.05
< 0
.05
< 0
.05
< 0
.02
0.06
< 0
.05
< 0
.05
< 0
.05
< 0
.02
0.12
< 0
.05
< 0
.05
< 0
.05
< 0
.02
463
260
4889
- - 8.
1
7.0
300
5520
4625
- - 24
,400
- - - - 16
,200
- - 22
25
0.03
- - - -
Tab
le
2
Che
mic
al
and
heav
y m
etal
ch
arac
teri
stic
s of
fee
d-w
ater
an
d br
ine
of d
esal
inat
ion
plan
ts,
the
UA
E
R
Para
met
er
Qid
fa
I Q
idfa
II
K
alba
Feed
B
rine
Fe
ed
Bri
ne
Che
mic
al
char
acte
rist
ics:
Cal
cium
(m
g/L
)
Mag
nesi
um
(mg/
L)
Sodi
um
(mg/
L)
Pota
ssiu
m
(mg/
L)
Stro
ntiu
m
(mg/
L)
Silic
on
as S
iOl
Silic
on
(mg/
L)
C o
f ca
tions
(m
e/L
)
PH
Bic
arbo
nate
(m
g/L
)
Chl
orid
e (m
g/L
)
Sulp
hate
(m
g/L
)
Nitr
ate
as N
(m
g/L
)
Nitr
ate
as N
O,
(mg/
L)
Fluo
ride
(m
g/L
)
2 of
ani
ons
(me/
L)
E.C
(m
S/cm
)
Ion
bala
nce
(me/
L)
SAR
(m
e/L
) SE
R (
me/
L)
Lan
gelie
r In
dex
(me/
L)
Ryz
ner
Inde
x (m
e/L
)
TD
S (
ma)
T
otal
io
ns (
mg/
L)
Tot
al
alka
linity
(m
g/L
)
Tot
al h
ardn
ess
(ma)
464
617
533
730
446
1180
63
6 76
0 17
3 48
20
2 16
40
2150
16
20
2240
24
5 64
4 21
40
2660
31
1 85
51
0
11,9
00
15,1
00
12,2
00
15,8
00
536
1170
14
,200
17
,700
19
30
498
3190
574.
0 76
7.0
581.
0 80
5.0
11.0
34
.1
661.
0 95
0.0
50.7
13
.2
84.5
4.56
7.
19
7.29
11
.50
5.05
10
.70
10.0
0 10
.40
14.2
0 3.
73
21.1
0 1.
07
1.07
15
.04
19.9
4 32
.30
82.7
9 1.
07
1.07
13
3.71
41
.82
164.
09
co.5
co
.5
7.03
9.
32
15.1
0 38
.70
co.5
0 co
.50
62.5
0 19
.50
76.7
0 69
0.44
88
4.18
70
5.47
92
8.65
66
.02
163.
65
842.
45
1051
.07
119.
48
31.3
9 19
2.98
7.87
6.
76
7.06
6.
97
7.48
7.
59
7.83
6.
38
7.66
7.
31
7.54
13
6 11
7 10
0 12
5 13
3 34
7 13
8 11
7 75
3 21
6 65
6 23
149
30,5
40
23,4
84
32,0
04
2103
54
13
27,0
98
34,8
39
2933
77
9 41
08
2787
39
31
3181
45
00
265
756
3121
46
02
1537
40
7 24
44
co.5
0.
7 0.
5 0.
7 4.
7 10
.7
0.6
0.8
3.6
1.1
6.2
c2.2
3.
0 3.
3 3.
1 20
.5
47.2
2.
5 3.
4 15
.9
4.8
27.4
1.5
2.1
0.6
0.9
co.1
co
.1
1.8
2.3
1.3
0.2
1.6
713.
40
945.
46
730.
43
998.
67
67.3
6 17
4.90
83
1.81
10
80.7
3 12
7.41
34
.08
178.
05
55,7
00
73,3
00
56,1
30
78,0
00
6190
15
,100
65
,900
81
,100
10
,850
33
00
14,9
60
-1.6
4 -3
.35
- 1.
74
-3.6
3 -1
.01
-3.3
2 0.
64
-1.3
9 -3
.21
-4.1
2 4.
02
58.2
2 64
.45
59.3
5 65
.42
5.06
6.
80
60.5
9 67
.95
20.3
0 10
.00
27.2
0
74.9
7 74
.29
75.2
3 74
.01
35.3
2 31
.10
73.3
2 73
.25
70.2
7 69
.02
71.9
1 1.
10
0.01
0.
15
0.30
0.
62
1.56
1.
20
-0.2
8 1.
26
-0.1
9 1.
04
5.67
6.
73
6.76
6.
37
6.29
4.
47
5.43
6.
93
5.14
7.
69
5.46
40,5
92
53,1
77
41,6
61
56,1
58
3700
94
32
47,9
4 1
61,5
87
7350
19
49
10,9
23
40,6
58
53,2
35
41,7
10
56,2
20
3765
96
02
48,0
09
61,6
45
7719
20
55
11,2
45
111
96
82
102
109
285
113
96
617
177
538
7922
10
,409
80
15
11,0
67
2130
56
15
10,4
18
12,8
71
1730
47
4 26
30
Hea
vy
met
al
char
acte
rist
ics:
Ir
on (
mg/
L)
0.22
0.
33
0.22
0.
35
Man
gane
se
(mg/
L)
< 0
.05
0.06
0.
06
0.07
Cop
per
(ma)
<
0.5
<
0.5
<
0.0
5 <
0.0
5
Zin
c (m
g/L
) <
0.5
<
0.5
<
0.0
5 <
0.0
5
Chr
omiu
m
(mg/
L)
< 0
.5
co.5
<
0.5
<
0.0
5
Feed
B
rine
< 0
.05
< 0
.05
< 0
.05
< 0
.05
< 0
.05
0.08
< 0
.05
< 0
.05
0.07
0.06
Jaba
l al
-Dha
na
Ham
riya
h U
mm
A
l-Q
wai
n
Feed
B
rine
B
rine
Fe
ed
Bri
ne
Feed
0.27
0.
37
0.05
<
0.0
5 0.
08
< 0
.05
0.05
0.
07
< 0
.05
< 0
.05
< 0
.05
< 0
.05
< 0
.05
< 0
.05
< 0
.05
< 0
.05
< 0
.05
< 0
.05
< 0
.05
< 0
.05
‘: 0
.05
< 0
.05
< 0
.05
< 0
.05
49
110
775
19.4
4.96
37
.01
%
17.3
0 $ 3
45.7
1 g
7.80
9
275
F
1182
56
2 2
1.8
B
s
7.7
f?
0.4
F’
3
49.7
0 46
80
$
-4.1
8 2
14.0
6 s
73.7
6 0.
40
5
7.00
5
2851
2986
226
581
< 0
.05
< 0
.05
< 0
.05
0.23
0.
12
0.26
M. Ahmed et al. /Desalination 133 (2001) 135-147 143
Table 3 Summary of observed brine disposal from plants in Oman and UAE
Plant
Adam, Oman
Haima, Oman
Esherjah, Oman
Sowqrah, Oman
Hitam, Oman
Mad&ah, Oman
Zahar, Oman
Assadanat, Oman
Abu-Mudhaibi, Oman
Safah, Oman
Qidfa 1, UAE
Qidfa II, UAE
Kalba, UAE
Umm Al-Qwain, UAE
Jabal Al-Dhana, UAE
Hamriayah, UAE
Al-Aryam, UAE
Al-Rafeek, UAE
Disposal method
Evaporation pond
Evaporation pond
Evaporation pond
Ocean disposal
Disposal to a bore
Disposal to the beach
Disposal to unlined bore
Disposal to unlined bore
Disposal to unlined bore
Disposal to lined evaporation ponds
Shoreline disposal
Comments
Leakage from the pond is suspected
Leakage from the pond is suspected
Holes were noticed in the liner
Potential for groundwater contamination
Potential for rapid groundwater contamination
Potential for groundwater contamination
Likelihood of groundwater contamination
Well-managed disposal system
No adverse impact on the shoreline was noticed other than the growth of green algae
Shoreline disposal No adverse impact on the shoreline was noticed other than the growth of green
Ocean disposal
Dumped in the nearby creek that ultimately reaches the ocean
Ocean disposal
Dumped in the creek far away from the feed-water source
Ocean disposal
Ocean disposal
Table 5 contains a list of chemicals used in RO desalination plants in Oman. The capacities of the 10 plants in Oman varied from 50 m3/d to a maximum of 1000m3/d. The salinity level of reject brine varied from 9.8 to 61.2dS/m. Groundwater tables were at depths between 40 to 80m from the surface. Heavy metals (Mn, Cu, Zn, and Cr) were found at trace levels in the concentrates. Various types of chemicals such as chlorine, sulphuric acid, sodium meta-bisulphite, lime powder, and citric acid are used in the RO plants in Oman. In the UAE, the plant capacities varied from 950 to 15,000m3/d. Both ground- water and seawater are used as feedwater,
depending on the location of the desalination plant. The salinity level in the brine of the UAE plants varied from 10.8 to 81 .l dS/m, while the sodium absorption ratio (SAR) varied from 6.8 to 68.0.
The newer plants in Oman have well-designed lined evaporation ponds whereas the older ones have unlined disposal pits. It appears that the lined evaporation ponds and disposal pits are not very effective. Lined-evaporation ponds prevent leakage resulting in increased concentration of salts and other chemicals in comparison to the wastewater that is dumped in the pond. Water samples collected from the evaporation pond in
144 M. Ahmed et al. /Desalination 133 (2001) 135-147
Table 4 Ratio of major ions of feed-water and brine of some Omani plants
Location
Adam
Haima
Esherjah
Hitam
Zahar
Assadanat
Abu- Mudhaibi
Chemical parameter
Ca (mg/L) Mg @g/L)
E$g%j SO, (WU EC (dS/m)
Ca (mg/L) MS (ma)
:;(g%j) SQ (mg/L) EC (dS/m)
Ca (m&) MS (ma) Na (mgn) Cl (mg/L) SQ (m&) EC (dS/m)
Ca (m&L) MS (m&) Na (ma) Cl (mg/L) SQ (mg/L) EC (dS/m)
Ca (ma) MS (ma)
$!g&) SO, (mg/L) EC (dS/m)
Ca (mg/L) MS (ma) Na (mg/L) Cl (ma) SO, (mg/L) EC (dS/m)
Ca (mgn) MS (mg/L) Na (m&L) Cl (m&L) SQ (m&L) EC (dS/m)
Feed- water
Brine Ratio (brine/ feed)
103 417 70 280 410 1,670 506 1,964 773 4,336 2.89 9.87
652 1,020 267 406 3,340 5,250 1,697 9,090 2,037 3,881 19.2 28.0
490 841 1,100 1,900 8,630 14,800 15,868 24,062 4,104 6,139 41.9 61.1
563 665 382 448 3,400 4,250 7,483 8,118 2,366 2,466 18.75 21.40
179 612 95 315 746 1,980 1,408 4,367 - 1,143 4.57 12.23
367 923 174 413 1,290 2,780 2,160 4,532 - 1,552 8.69 16.8
294 962 137 4,48 1,360 4,630 2,151 7,335 515 3,296 7.8 23.4
4.05 4.00 4.07 3.88 5.61 3.42
1.56 1.52 1.57 5.36 1.91 1.46
1.72 1.73 1.72 1.52 1.50 1.46
1.18 1.17 1.25 1.08 1.04 1.14
3.42 3.32 2.65 3.10
z68
2.51 2.37 2.15 2.10 - 1.93
3.27 3.27 3.40 3.41 6.40 3.00
Haima and the disposal pits in Assadanat and Abu-Mudhaibi showed little or no increase in the concentrations of salts (Table 6).
It was also observed during the field visits that some of the recently constructed evaporation ponds had leaks. There were some clear indi- cations that leakage from some of the ponds and pits existed since no salt build-up was noticed in these structures and the volumes of standing water were very small. Further in-depth investi- gations through water balance studies and the monitoring of the underlying groundwater aquifers should enable the detection of any significant leakages from such structures.
5. Construction cost
Very little information is available on the cost of disposal from the plants visited. The Ministry of Electricity and Water in Oman provided data on construction costs of five recently built evapo- ration ponds (Table 7). From the table, it is clear that the unit cost of construction is reduced as the pond size increases. However, there are several other factors involved. Such factors include the remoteness of the plant location, distance to nearby towns, availability of local construction materials, and labor.
6. Challenges and opportunities of brine disposal methods
Various options exist for the disposal of reject brine from inland desalination plants. These include waste minimization, discharge to surface water, discharge to wastewater treatment plants, deep wells, land application, evaporation ponds, and wastewater evaporators. Waste minimization is an approach in which the objective is to produce less concentrate (generally by mem- brane-process recovery-enhancement techniques) or to reduce the concentrators prior to ultimate
Table 5
M. Ahmed et al. /Desalination 133 (2001) 135-147 145
Chemicals used in RO desalination plants in Oman
Plant name
Adam
Haima
Esherjah
Sowqrah
Hitam
Mad&ah
Zahar
Assadanat
Treatment of feed- water
Treatment of produced water
Chemicals used in cleaning Post-cleaning Others treatment
Sulphuric acid, Chlorine, chlorine, Flocon- 100, lime powder sodium meta bisulphite
Sulphuric acid, sodium meta bisulphite, Flocon- 100, chlorine Flocon-100, sodium meta bisulphite Chlorine, Flocon- 100, sodium meta bisulphite Chlorine, Flocon- 100, sodium meta bisulphite Sulphuric acid
Sodium meta bisulphite, Flocon- 100 Sodium meta bisulphite, Flocon- 100
Chlorine, lime powder
Chlorine, lime powder Chlorine, lime powder
Chlorine, limestone
Chlorine, limestone
Formaline
Chlorine, EDTA, citric acid, sodium limestone hydroxide
Chlorine, limestone
Abu Mudhaibi Sulphuric acid, sodium meta bisulphite
Khumkham Sulphuric acid, Flocon-100, polyelectrolyte, sodium meta bisulphite
Chlorine, limestone
Chlorine, lime powder
Citric acid, EDTA, trisodium phosphate, sodium tripoly phosphate
EDTA, citric acid, ammonia, sodium hydroxide
EDTA, citric acid, sodium hydroxide, ammonia
EDTA, sodium hydroxide, citric acid
Citric acid, sodium hydroxide, Sodium dodecyle sulphate
EDTA, citric acid, sodium hydroxide
EDTA, citric acid, ammonia
PT-A, PT-B
PT-A, PT-B
PT-A, PT-B Perma clean sodium hexameta phosphate
disposal [3]. This particular approach is not usually very economical since the increase in cost is substantial, given the need for an extensive pretreatment and the increased membrane area. Although the volume is reduced, the concentration of various minerals and chemicals increases. Such high concentrations can create special problems with disposal since many
disposal regulations are based on concentrations, not volume.
Under certain conditions, brine from desali- nation plants can have useful applications. Production of salt and other minerals (Mg) are the most obvious. Al-Mutaz and Wagialla [lo] reported that caustic soda can be produced from desalination brines at a cost of about 149 $US/t.
146
Table 6
M. Ahmed et al. /Desalination 133 (2001) 135-147
Ratio of water quality parameters (disposal pond water vs. wastewater)
Location
Haima
Assadanat
Abu-Mudhaibi
Parameter
Ca (mg/L) Mg (mg/L) Na (mg/L) CL (ma) SO, (ma) Fe (ma) EC (dS/m)
Ca (mgk) Mg (mg/L) Na (mga) Cl (mgQ SQ (ma) Pe (mg/L) EC (dS/m)
Ca (mg/L) Mg (mg/L) Na (m@) Cl (ma) SD, (mgk) Fe (mg/L) EC (dS/m)
Wastewater Pond water
1020 1100 406 438 5250 5870 9090 9661 3881 3881 0.14 0.18 28.0 30.2
923 871 0.94 413 413 1.00 2780 2790 1 .oo 4532 4717 1.04 1552 1578 1.02 0.06 0.07 1.17 16.8 16.9 1.00
962 929 448 438 4630 4430 7335 9006 3296 3059 0.12 0.12 23.4 23.15
Ratio
1.08 1.08 1.12 1.06 1.00 1.29 1.08
0.97 0.98 0.96 1.23 0.93 1.00 0.99
Table 7 Cost of disposal (evaporation pond construction in Oman)
Plant
Adam
Haima
Esherjah
Al-Haj
Khum-khan-r
Capacity Recovery (m id) rate (%)
1000 75
100 38
100 42
100 40
100 45
Design reject brine production (m3/d)
333
163
138
150
122
cost of construction (SUS)
384,157
121,360
184,766
153,423
65,629
Pond Unit cost Unit cost per size (m’) ($US/m’) ;zneof reject
($US/m’/d)
57,600 6.7 1154
15,041 8.1 745
13,200 15.0 339
13,200 11.6 1023
1,200 54.7 538
The use of evaporation ponds for brine shrimp possible provided that soil salinization is main- cultivation has been attempted in Australia. tained at acceptable levels by controlling Evaporation ponds are ideal places for brine- leaching and minimizing the risk of groundwater shrimp production since no food competitors or contamination. Soil solutions composed of high predators survive at high salinity, resulting in a solute concentrations (salinity), or dominated by mono-culture under natural conditions. Irrigation calcium and magnesium salts, are conducive to of salt-tolerant plants by reject brine will also be good soil physical properties. Conversely, low
A4. Ahmed et al. /Desalination 133 (2001) 135-147 147
salt concentrations and relatively high propor- tions of sodium salts adversely affect permeability and tilth [ 111.
The salinity of brine from desalination plants in Oman and the UAE is very high and so is the SAR. However, the amount of brine in Oman is relatively small. Considering that the rate of evaporation in Oman and the UAE is extremely high, it is unlikely that any large-scale use of brine (from desalination plants) for irrigation will be feasible. Other uses of brine are unlikely for the following reasons: the volume of brine produced is relatively small in many plants, most of the desalination plants are located in the desert far from big towns, and the environmental concerns related to any product produced or extracted from brine are high.
7. Conclusions
The small-scale RO desalination plants in Oman use mostly lined evaporation ponds and unlined pits for the disposal ofbrine. Considering the high salt concentrations and the presence of other chemicals, it is imperative that safe methods of disposal be used for the protection of groundwater resources. Evaporation ponds (lined) and disposal pits did not show any noticeable increase in the concentration of various salts and EC levels. This is an indication that brine could be reaching the groundwater. In the UAE, the RO plants investigated dispose their brine in the sea. Due to technical, environmental, and economic constraints, it is unlikely that the brine reject from desalination plants can be used for any meaningful purposes in Oman and the UAE. As such, well designed and well constructed evaporation ponds under proper management will be the most appropriate disposal mechanism for inland desalination plants in Oman, while disposal to the sea will likely continue for foreseeable future in the UAE.
Acknowledgements
This study was made possible partially through funding from the Middle East Desali- nation Research Center under contract number 98-R-004. The authors would also like to acknowledge the valuable assistance provided by the Omani Ministry of Water Resources, the Omani Ministry of Electricity and Water, Oman National Electricity Company, and the UAE Ministry of Water and Electricity.
References
PI
PI
131
[41
PI
161
[71
181
191
[lOI
1111
T.M.A. Al-Sajwani and R.J. Lawrence, Proc., Intemat. Conf. on Water Resources Management in Arid Countries, Muscat, 1995, pp. 617626. H. Khordagui, Environmental aspects of brine reject from desalination industry in the ESCWA region. ESCWA, Beirut, 1997. M. Mickley, R. Hamilton, L. Gallegos and J. Truesdall, membrane concentration disposal, AWWA Research Foundation, Denver, 1993. ESCWA, Water desalination: the experience of GCC countries, in: Regional Symposium on Water Use and Conservation, Report E/ESCWAlNR/1993/ WG.lAVP.10, Amman, 1993. P. Glue&stern and M. Priel, Desalination, 108 (1996) 19. J. Truesdall, M. Mickley and R. Hamilton, Desalination, 102 (1995) 93. A.I. Alaabdula’aly and A.J. Al-%&i, Disposal in groundwater RO plants in the central region of Saudi Arabia, Proc., IDA Conference, Abu Dhabi, 1995. M. Mickley, Environmental considerations for the disposal of desalination concentrates, Proc., IDA Conference, Abu Dhabi, 1995. D. Squire, J. Murrer, P. Holden and C. Fitzpatrick, Desalination, 108 (1996) 143. I.S. Al-Mutaz and K.M. Wagialla, Desalination, 69 (1988) 297. J.D. Rhodes, A. Kandiah and A.M. Mashali, The use of saline waters for crop production, FAO Irrigation and Drainage, paper 48, Rome, 1992.